Gravimetric Sulfate Determination
GRAVIMETRIC DETERMINATION OF SULFATE
Purpose
You will be given a solid powder, which has been dried to constant mass. The sample is water soluble. The purpose of this experiment is to determine the concentration of sulfate in your solid sample using gravimetric analysis.
Background
Gravimetric Analysis
The goal of most quantitative chemical analysis measurements is to estimate the relative abundance of an analyte in a chemical sample. For solid and liquid samples, a very common expression of analyte content is based on the mass fraction. This fraction is commonly expressed as a percentage (w/w %), as parts per million (ppm) or as parts per billion (ppb), depending on the concentration level of the analyte. Classical chemical analysis methods are excellent for the determination of analyte concentrations in the range of 1−100 w/w %. In order to estimate the analyte mass fraction of any solid sample, we typically need two measurements, one to estimate the sample mass and one to estimate the analyte mass. In gravimetric analysis, measurements of mass are used to determine the analyte concentration in a sample. In the most common form of gravimetric analysis, the analyte is separated from the rest of the sample in the form of a solid precipitate. In this experiment, the analysis of sulfate is performed using barium chloride as a reagent to precipitate sulfate from the dissolved sample. The mass of sulfate in the sample can be calculated by simple stoichiometry from the mass of the weighing form of the sulfate precipitate. In order to ensure maximum filterability and minimum contamination, the sulfate is precipitated under conditions that maximize the particle size. These conditions include: (a) avoiding excessively high concentrations of precipitating reagent; (b) slow addition of reagent to a hot solution, with vigorous stirring; (c) avoiding a great excess of reagent. The digestion of the precipitant after the reaction minimizes errors due to coprecipitation.
Purpose
You will be given a solid powder, which has been dried to constant mass. The sample is water soluble. The purpose of this experiment is to determine the concentration of sulfate in your solid sample using gravimetric analysis.
Background
Gravimetric Analysis
The goal of most quantitative chemical analysis measurements is to estimate the relative abundance of an analyte in a chemical sample. For solid and liquid samples, a very common expression of analyte content is based on the mass fraction. This fraction is commonly expressed as a percentage (w/w %), as parts per million (ppm) or as parts per billion (ppb), depending on the concentration level of the analyte. Classical chemical analysis methods are excellent for the determination of analyte concentrations in the range of 1−100 w/w %. In order to estimate the analyte mass fraction of any solid sample, we typically need two measurements, one to estimate the sample mass and one to estimate the analyte mass. In gravimetric analysis, measurements of mass are used to determine the analyte concentration in a sample. In the most common form of gravimetric analysis, the analyte is separated from the rest of the sample in the form of a solid precipitate. In this experiment, the analysis of sulfate is performed using barium chloride as a reagent to precipitate sulfate from the dissolved sample. The mass of sulfate in the sample can be calculated by simple stoichiometry from the mass of the weighing form of the sulfate precipitate. In order to ensure maximum filterability and minimum contamination, the sulfate is precipitated under conditions that maximize the particle size. These conditions include: (a) avoiding excessively high concentrations of precipitating reagent; (b) slow addition of reagent to a hot solution, with vigorous stirring; (c) avoiding a great excess of reagent. The digestion of the precipitant after the reaction minimizes errors due to coprecipitation.